This invention relates to a method for making a modular energy-absorbing member for decelerating an object that impacts the member or the assembly in which the member is placed.
In many fields it is desirable to provide assemblies which are able to decelerate, in a given, limited distance, an object which impacts the assembly. To do so, the assembly must absorb a significant percentage of the impact energy transferred by the object. In the past, this has been accomplished physically by providing the assembly with an energy-absorbing member for supporting deformation of the assembly in order to absorb the energy of the impacting object. Alternative approaches are exemplified by commonly owned U.S. Pat. No. 5,700,545; U.S. Ser. No. 09/018,666, filed on Feb. 4, 1998 (now U.S. Pat. No. 6,017,084); and U.S. Ser. No. 09/328,196, filed on Jun. 8, 1999, incorporated herein by reference.
Within a vehicle, for example, occupants require protection from impact with interior components such as the pillars and headrails. These structures are typically made of steel tubing or steel channels which are welded together to form the structural cage or unitized body for the vehicle. Designers have attempted to place energy-absorbers over the pillars, headrails and other parts of a vehicle to protect the vehicle occupants. Prior art approaches are found in the use of energy-absorbing urethanes, rigid polymeric foams, blocks or cells or vanes of engineered plastics, various sheet metal configurations, metal beams, honeycombed metal, and other geometric solids. Most of these materials, however, while crushing generally absorb less than the desired amount of energy for a given displacement.
The desired response of an energy-absorbing material from initial loading to failure is one wherein a near xe2x80x9csquare wavexe2x80x9d response of force versus deflection is produced, such that the force exerted on the decelerated object is nearly unchanged over a desired range of crush distance or deflection. Commonly owned U.S. Pat. No. 5,700,545 issued to Audi et al. discloses such an energy-absorbing structure. The energy-absorbing member disclosed therein comprises an array of material, such as expanded metal, configured with vertical supporting faces which are generally orthogonal to spacing faces lying in the plane of an incident surface. While the energy-absorption characteristics of such a structure are improved compared with those of the prior art, due to its configuration only the supporting faces, representing xcx9c50% of the absorbing member, are utilized in energy-absorption. The spacing faces play little or no part in energy-absorption since they generally lie in a plane orthogonal to the direction of impact.
Therefore, a need exists for providing a method for making an energy-absorbing assembly which maximizes the use of energy-absorbing members, so that maximum collapsible material is harnessed to produce superior energy-absorbing characteristics and optimize the amount of energy-absorbed per unit mass and per unit deflection of the energy-absorbing member, compared with prior art structures.
The amount of energy that is desired to be absorbed by the absorbing assembly depends on the kinetic energy of the object to be decelerated and the deflection of the background structure when impacted by the object. In the case of automotive interiors, the automobile body or cage deflects to a degree when impacted by occupants. The degree of deflection varies through the vehicle cage for a given amount of impact energy. So the energy-absorbing structure is required to absorb different amounts of energy at different locations in the vehicle. The amount of crush space available also varies.
Thus, it would be desirable, additionally to provide a method for making a modular energy-absorbing assembly wherein constituent modules offer different degrees of resistance to impact forces. Further, it would be useful to provide such a module wherein the material which supports each module is itself formed from an energy-absorbing structure.
It is an object of the present invention to provide a method for making a modular energy-absorbing assembly which decelerates an impacting object in a given, limited distance after engagement with the assembly, wherein various modules or areas of the assembly offer different degrees of resistance to impact forces, thereby allowing the designer to customize the assembly according to the requirements of the environment in which it is deployed.
It is another object of the present invention to form holders integral in the assembly in which wires, tubes, ducts, etc. may be placed without the need to use additional attachments such as clips, adhesives, etc.
It is a further object of the present invention to provide a method for making an energy-absorbing assembly that maximizes the energy-absorption over a given distance as compared with prior art structures, while affording economies in manufacturing.
It is a still further object of the present invention to provide a method for making an energy-absorbing assembly which absorbs energy in a near square-wave manner.
It is another object of the present invention to provide a method for making an energy-absorbing assembly which is adapted for mounting on a vehicle in order to provide impact protection.
Accordingly, a method for making a thermoformed energy-absorbing assembly is provided for decelerating an object that impacts the assembly. The assembly includes a base and at least one energy-absorbing module associated with the base for accommodating deformation of the assembly. The at least one energy-absorbing module comprises a structure selected from the group consisting of a first structure, termed herein as structure (A) and a second structure, termed herein as structure (B). Structure (A) comprises a lattice of interconnected strands, the strands intersecting to define a plurality of cells and being supported within a channel formed within the base. The structure (A) is oriented such that the plane of each cell is substantially parallel to the impacting force in order to maximize energy-absorption over a given distance. The lattice collapses and at least some of the cells become at least partially closed during energy-absorption.
The modules may be separate pieces or modular sections or merely areas of the same piece may be designed with varying absorbing characteristics between them. Alternatively, each piece may be designed to have the same absorbing characteristics. Pieces of different designs may then be placed next to or in close proximity to each other to afford a generally continual energy-absorbing function.
Structure (B) includes a plurality of cup-or other-shaped recesses, each having a floor and a frusto-conical wall defined within the base. The structure (B) is oriented such that the floor of each cup is substantially orthogonal to the impacting force. Its frusto-conical wall is substantially parallel to the impacting force in order to maximize energy-absorption by the wall over a given distance. The wall at least partially collapses and at least some of the cups become at least partially compressed during energy-absorption. The shape of the cups in the structure (B) in the plan view may be circular, oval, triangular, hexagonal or any other polygonal shape.
Structures (A) and (B) afford the designer a user-determinable resistance to impacting forces.